backing up the account table from the realm DB will not get the characters over. It only brings over the accounts and passwords. The account table is only "Linked" to the character table (in the MaNGOS DB). Which is then linked to about 6 other tables that hold specific data about each character. (Items, guilds... the list goes on)
To the first post:
Let me get this right, you have two databases that you are trying to consolidate into one basically?
If that is the case you aren't going to be able to do it easily. Every time MaNGOS makes a new entry it does it incrimentally. So lets say you both have only one account on both servers. Now your account and players actually hold the same account ID that his account and players do. So in each of the tables that are linked together you have to change each ID on all characters linked to that account. Its like the first column of data for each character.
If this is the only account on the server, not really a problem to do, you can export each line as a comma separated value, save it to an "Excel" friendly format, mod it there and then take it to his PC. Then you could import it there as a CSV and if all the data was done right, you should have your toons and account on his PC.
Hope this helps, and I also hope it doesn't steer you clear of the challenge. Just need some direction on what lines to get, which I'm sorry to say I don't know which ones to get for you.